In the weighing art, it is known to obtain a precise weight of a product formed of a plurality of individual articles having various weights, each of which is a significant fraction of the total desired weight, by the use of "combination weighing devices". Such devices are disclosed, for example, in U.S. Pat. No. 3,939,928 to Murakami et al, and in U.S. Pat. No. 4,267,894 to Hirano et al.
In the Murakami et al patent a number of objects are fed to each of a plurality of weighing hoppers. A complicated electronic circuit is used to test successive combinations of hoppers for a combined weight lower than the previously achieved best weight. The circuit thus ultimately provides a combination having a weight whose deviation from the desired weight is minimal over all possible combinations of hoppers. Objects from the appropriately selected hoppers are delivered to a pool hopper, from whence the objects are discharged to be collected in a bucket. In a particular example, eight weighing machines are used, and a single object is loaded into each such weighing machine. A total of 154 combinations of hoppers for the weighing machines are tested by limiting the number of objects to be taken out to be 4, 5 or 6.
In the Hirano et al improvement on the '928 teaching, a predetermined number of articles is loaded into each of the weighing balances provided. An adding circuit receives as a negative input the intended weight to be obtained, and positive inputs from each of a plurality of holding circuits storing the weights in the balances. A combination generator is provided for gating the outputs of sequential combinations of balances to the adder. The output of the adder is compared with upper and lower deviation limits for the intended weight. If the output of the adder is within the accepted deviation, the selected combination is stored in a combination memory and the adder output used to update the acceptable upper limit of the intended weight. That is, each combination of balances determined to have an acceptable product weight is used to narrow the acceptable deviation limits, thereby arriving at a combination storing the weight closest to the intended weight.
As is apparent from the above summaries, the prior art generates substantially all combinations of balances or hoppers to test all combinations of weights against the desired weight. Such generation is inefficient, and arises particularly from the fact that the items provided into the balances, or weighing hoppers, are not in themselves preweighed. Further, by seeking the best combination of hoppers, needless time is wasted in comparison of the repetitive combinations when an acceptable combination may have already been found. Still further, such prior art approaches provide no solution for the problem arising when none of the tested combinations meets the acceptable deviation from the desired weight. The prior disclosures further suffer from the deficiency of inefficient use of scale and weighing apparatus, in which several scales are each used to provide the product to but a single hopper. The weighing devices remain idle during most of the operation of such combination weighers.
There is thus a need for a combination weighing device having simplified electronic circuitry which generates combinations of only a predetermined number of storage cups, rather than of all possible combinations of storage cups, for more rapidly reaching a decision as to acceptable combinations. Additionally, a combination weighing apparatus having simplified circuitry for rapidly determining an acceptable combination is needed, as well as such a system in which weighing devices are efficiently used.